In February, millions of dollars worth of jewelry was stolen in Berlin. Two of the suspects are identical (monozygotic) twins, Hassan and Abbas O. DNA analysis showed that one or both of them were probably at the scene of the crime but it’s impossible to tell. If only one of the brothers is guilty, investigators can’t tell for sure which one it is.

In reality, identical twins do not have perfectly identical DNA due to epigenomic chemical modifications and DNA copy number variations. But until more sophisticated DNA analyses become more widely available or other evidence comes to light, Hassan and Abbas are free and have not been charged. (Spiegel Online via Boing Boing)

Identical twins be forewarned. You may be able to get away with it now, but your time is coming.

NB: In Malaysia, investigators were unable to figure out which one of a pair of identical twins trafficked 166 kilograms of cannabis and 1.7 kilograms of opium. A judge dismissed the case and both twins were set free. (Telegraph)

Congratulations to New York Times reporter Amy Harmon on her Pulitzer Prize for The DNA Age series of articles on “the impact of genetic technology on American life.”

Congratulations also to TR Gregory at Genomicron on his one-year blogging anniversary!

Lee Lofland, author of Police Procedure and Investigation, A Guide for Writers shares Things Writers Should Know about DNA. I just have on nitpicky point about the DNA fact that “identical twins have identical DNA”…erm, not quite .

Identical (monozygotic) twins Raymon and Richard Miller had better watch out. The two were embroiled in a paternity suit that alleged both had slept with the same woman on the same day and nobody knew which brother had impregnated her. In May 2007, the judge decided that Raymon is the legal father of the child who was subsequently born although child support was split between the two brothers.

Standard paternity testing examines 16 DNA markers which is enough to make them over 99.99% accurate. In the case of the State of Missouri and Holly Marie Adams vs. Raymon and Richard Miller, the paternity test showed that the two brothers both had a 99.999% probability of being the father. There is currently no commercially available test that can determine which of the twin brothers passed his DNA to the child even though there are ways in which the genomes of identical twins differ.

Epigenomic chemical modifications. Researchers at Ohio State University found epigenetic changes in twins’ genomes that increased as pairs of twins aged. One of the main epigenetic processes that occurs to our DNA is methylation which can be caused by environmental exposures, such as diet and physical activity. Methylation can lead to differences in gene expression and as we age, the amount of DNA methylation increases. So, it’s expected that identical twins will grow less and less similar in their patterns of DNA methylation and gene expression as their lives progress especially if their lifestyle habits and surroundings differ greatly.

DNA copy-number-variation profiles. Another way in which the genomes of identical twins may differ is in copy number variation (CNV) that appears as segments of DNA that are missing, occur in multiple copies, or have flipped orientation in the genome. Identical (monozygotic) twins have been found to have different CNVs which could explain why even identical twins are not truly identical in appearance or other physical characteristics despite similar environmental exposures. For example, one twin sometimes develops a disease while the other does not. (HT: DNA Direct Talk)

What does this mean for Raymon and Richard Miller? DNA methylation patterns and copy number variations can be definitive in a paternity case if differences between the brothers are identified. Then, by comparing the same genomic regions in the child, it may be possible to see who the s/he more closely resembles genetically keeping in mind that the child is also accumulating his/her own DNA methylation and CNVs. While this type of genetic analysis isn’t currently available, it will most likely be available in the child’s lifetime. I would suggest that the Millers’ love child or his/her guardian store DNA from Raymon and Richard Miller for future analysis.

DNA profiling was discovered in 1984 by geneticist Alec Jeffreys of Britain’s Leicester University, who first used it three years later to help solve the murders of Leicestershire schoolgirls Dawn Ashworth and Lynda Mann.

Hereâ€™s a very basic description of how DNA fingerprints were first created using restriction fragment length polymorphisms (RFLP):

1. Extract a sample of DNA from blood, hair, skin, cheek cells, etc.
2. Use polymerase chain reaction (PCR) to create more copies of the DNA to analyze.
3. Use restriction enzymes to cut the DNA strand at specific sequences, which will result in pieces of DNA of varying sizes. Since each personâ€™s DNA unique, the enzymes will cut the DNA in different places and varying sizes of DNA pieces will result.
4. The small pieces of DNA will be passed through an agarose gel which separates them according to size.
5. Compare the DNA patterns created.

The technology makes use of the fact that small sections of DNA repeat themselves over and over in a way that is unique to each individual. The length of repeats can be measured at different locations to build up an individual’s profile.

Modern genetic tests typically look at 20 “marker” sections of DNA — 10 from the maternal and 10 from the paternal line. The chance of two strangers matching on all 20 is less than one in 1 billion. The chance of a match with a relative, though, is much higher and identical twins have identical profiles.

I’m not really sure what 20 markers this fact is referring to. Law enforcement relies on the Combined DNA Index System (CODIS) that creates DNA profiles from 13 core STR markers. Paternity tests examine as little as three markers to as many as 16. The genotypes at each of the markers would consist of data on two alleles – one from the mother and one from the father.

Scientists collect DNA direct from suspects, using a mouth swab, or from the scene of a crime, by gathering traces of blood, semen, hair or saliva. Crime scene samples are more difficult to analyze, since they may be very small and can contain the DNA of several people.

I don’t have much to say about this except that sometimes samples are just plain difficult to analyze whether or not it’s from a crime scene. It all depends on the sample from which the DNA is extracted and the informativeness of the markers being analyzed.

Governments around the world are building up DNA databases to match suspects with evidence. The United States has the largest database, with over 5 million profiles. But Britain has the highest proportion of people catalogued, with its 4 million records equal to more than 6 percent of the population.

As points of reference, Australia’s national DNA database has over 350,000 DNA samples while New York State has almost 250,000. You may also be interested in these previous posts about the UK national database:

If one parent is bipolar, there is a 7 to 10 percent higher risk of getting bipolar disorder.

If there are two parents, there is a 20 percent chance of developing bipolar in the offspring because of the multiple genes.

The Slynar, FAT, and P2RX7 genes are the only three genes thus far to be associated with bipolar disorder.

On a related note, similar to the mania phase of bipolar illness, a person experiencing hypomania is overflowing with energy, ebullience, and excitement. Hypomanic people often accomplish great things and are persuasive leaders. Dr. John Gartner, assistant professor of psychiatry at Johns Hopkins School of Medicine, claims in The Hypomanic Edge that a higher than expected number of Americans are hypomanic, which may be explained by genetics.

America is the land of immigrants and studies have shown that the prevalence of bipolar disorder is higher among this population. In turn, the descendents of these immigrants have a higher risk of hypomania. People affected by bipolar disorder or hypomania may be more willing to risk leaving their home country for a strange, foreign land because they feel invincibile while in their heightened state.

DNA Direct has a new VP Clinical Affairs, Trisha Brown, and a new Clinical Director, Cynthia Kane. Read more about them in this press release (pdf). (By now you all know I work for them, right?)

Nicholas Wade of The New York Times explores moral rules in Is “Do Unto Others” Written Into Our Genes? (HT: Tom Head) Lee Dye wrote a similar article in 2005–Are We Programmed for Kindness?–that mentioned Dr. Philippe Rushton of the University of Western Ontario who conducted a study of 174 pairs of identical twins and 148 pairs of fraternal twins. Results showed that genes account for 42 percent of individual difference in attitudes. But Stanford’s Paul Erlich disagreed:

Genetic evolution did not determine most of how we act or provide us all with a pre-programmed “human nature.” There is no reason to believe that human beings are either innately violent or innately peaceful, instinctively disposed to wreck their environments or to be conservationists, or born genetically gay or genetically straight.

The OR7D4 gene has been linked to people’s perceptions of human body odor (B.O. in common parlance). Two variants of the OR7D4 gene exist; people with one variant thought androstenone–a testosterone-derived steroid found in human urine and sweat–smelled like “old cat pee” while the group with the other variant thought it smelled like “sweet vanilla.” Which group do you think you belong to?

I’m on vacation this week but that doesn’t mean Eye on DNA is going to be silent. I’ve prepared posts in advance and figured this list of 100 facts about DNA should keep you busy! It’s not particularly well-organized since I created using stream of consciousness. Ommm.

Answer: Humans have 46 chromosomes, horses have 64, and donkeys have 62.

Although that’s an interesting bit of DNA trivia to know, it’s even more interesting in the context of breeding between horses and donkeys. If a horse breeds with a donkey, they end up with sterile offspring that have 63 chrosomes – 32 chromsomes from the horse parent and 31 from from the donkey parent. Horse-donkey offspring aka mules are sterile because their odd number of chromosomes makes it technically difficult for chromosomes to pair up properly during the process of meiosis (cell divison of sperm and eggs). This should mean that mules cannot reproduce.

A female mule in Colorado has beaten insurmountable odds and given birth to a foal . According to Laura and Larry Amos, the owners, there have only been about 50 cases of mules giving birth in the past 200 years and only two have been verified using DNA testing. A previous case of twins born of a mule was made possible by hemiclonal transmission; the father’s chromosomes were silenced and shut down completely. Initial DNA tests on the foal and mother mule-in-question showed that Kate, the female mule, was definitely the mother. Results from a count of the foal’s chromosomes are not yet available. No clue on the possible father.

All parents want to protect their children from harm especially when it comes to serious illnesses. For families who have a history of inherited diseases, there is now the option of preimplantation genetic diagnosis (PGD) where one cell is taken from an early stage embryo and genetically screened for the disease-causing mutation. Currently, PGD can be performed for a long list of diseases including Huntington’s disease, breast cancer, neurofibromatosis, cystic fibrosis, and polycystic kidney disease.

This past weekend, the Brookhyser family was profiled in The Orange County Register. Stacy Brookhyser carries the Huntington’s disease (HD) gene and not only is she destined to develop the disease herself later in life, she has a 50-50 chance of passing on the gene to each child. But with the help of PGD, she and her husband were able to select embryos that are free of the HD gene and now have two healthy twin girls.

Last year, a reader in Malaysia, under the pseudonym Rica Lode, contacted me asking for more information on PGD for neurofibromatosis (NF) type I. Here’s what she said about their search for PGD (reprinted here with permission):

I am in my 30s, born and bred in Malaysia. Iâ€™ve been married for a few years now with no children yet. I would never imagine one day how genetics would play a strong role in our lives. Genetics, bioethics has never been a part of my vocabulary before until I came across this term, preimplantation genetic diagnosis in the newspapers recently. It appears to be the latest â€œwordâ€ in the world due to â€œdesigner babiesâ€. This procedure allows parents to select the gender of their baby effortlessly.

To me and my husband, itâ€™s a God-send solution to our dilemma. Because this procedure ensures we would have a healthy child as it is able to detect genetic disorder. My husband have a genetic disorder condition known as Neurofibromatosis Type I, where benign tumours would grow externally and/ internally on the peripheral nerves. It is a gene mutation on chromosome 17. Thereâ€™s no known cure. Thereâ€™s a 50% chance this would passed onto our next of kin.

Rica and her husband searched all over Asia for affordable and available PGD. The situation is much the same in Europe. At the annual meeting of the European Society of Human Reproduction and Embryology, a study on PGD patients travelling abroad for treatment found that patients had the following reasons for searching internationally:

PGD was banned in their own country (PGD is banned in Ireland, Switzerland and Germany.)

Quality of treatment

Test availability

Expertise in certain diseases

Cost and length of waiting lists in their home countries

According to the study, the situation is untenable for both healthcare providers and patients where free exchange of information is impossible. Doctors are afraid of being prosecuted and patients aren’t able to access all the medical treatment, counselling, and support they need once they leave the country where PGD was performed. Mr. Lawford Davies, a solicitor specialising in reproductive and genetic technologies, recommends that members of the European Union develop a consistent policy across all countries and regulate rather than prohibit PGD. (HT: PHG Foundation)

In the end, elective procedures like PGD will be subject not only to legal restrictions, but also to market forces. Medical tourism is an increasingly lucrative business for the uninsured and the underinsured. There may not be a way around this but at least the procedure is available somewhere somehow.